That would depend on a couple of things:
Are there any significant sources of moisture - bathtub / shower stall?
If so, and the toilet area is completely enclosed (walls / door) than installation of another exhaust fan closer / above those bathroom fixtures would be advisable. Technically (by code) an exhaust fan is not required if bathroom equipped with properly sized openable window.
If the toilet area has no doors, just surrounded with walls, you could probably get away with the existing bathroom exhaust fan if it’s large enough (CFM) to provide the minimum required amount of air exchanges.